| 摘要 |
Process for coating a moving substrate with a thermoplastic film in predefined zones of varying thickness comprises (a) selectively controlling the thickness of the thermoplastic material flowing through the extrusion die head before its exit from the extrusion die, (b) forming the material into a film with a predefined profile thickness, and (c) extruding the thermoplastic material in the form of the profiled film obtained in the die head so as to become deposited on the moving substrate. The profile obtained in the extruded film is formed selectively with the aid of a dosing rod (37) placed inside the die head, this rod (37) having a plurality of segments provided with helical grooves of differing depth. The plastic material is pref. polyethylene. The substrate may consist of paper cardboard, glassine, cellophane, plastic film, metal foil, fabric or glass fibres. The thermoplastic film is placed on the substrate in a plurality of zones of varying thickness, to form a prefined arrangement on predefined areas of the substrate surface. The substrate is pref. a blank for a container. The blank is pref. provided with thick film zones with a thickness of 0.025-0.05 mn zones with a thickness of 0.02-0.028 mm, and thin zones with a thickness of 0.01-0.03 mm. The process enables cardboard container blanks to be selectively coated with a thermoplastic material to form areas of varying thickness. Liquid tight containers, e.g. for milk, can be produced with lower usage of thermoplastic materials as the film has a varying thickness, depending on practical requirements. |
